U.S. Pat. No. 7,156,006 discloses a turning insert for a machine tool that is holding a rotating workpiece, the turning insert being brought into cutting engagement with the workpiece and simultaneously rotating around its own axis. The rotating turning insert is held in a rotary tool holder. The front surface of the rotating turning insert is formed as a chip surface and may include means for breaking the chips formed in the machining.
U.S. Pat. No. 7,325,471 discloses a turning insert similar to the one disclosed in U.S. Pat. No. 7,156,006 and intended to be used in a similar machine tool.
In conventional turning machining, where the turning insert is stationary, i.e., does not rotate around its own axis, the same area of the turning insert will be in engagement with the workpiece during the entire turning operation. This means that the heating of this area becomes high and that the wear of the same area thereby becomes great. This in turn affects the service life negatively.
By allowing the turning insert to rotate around its own axis, the part of the cutting edge that is in engagement with the workpiece will be displaced continuously so that new cutting edge is fed forward all the time. In such a way, the part of the cutting edge that is in engagement with the workpiece is given the possibility of cooling down, whereby the temperature at the cutting edge can be kept on a lower level than in conventional turning. This means that the service life of the tool can increase. Alternatively, the intensity of the machining can be increased at a maintained high temperature. A longer service life has great advantages since the turning operation can be carried out with no or fewer replacements of turning inserts. In addition to the higher efficiency and the economic benefits achieved thereby, this is advantageous since it is difficult to avoid irregularities in the machined surface after a replacement of a turning insert.
The technique disclosed in the above-mentioned U.S. Pat. No. 7,156,006 has the disadvantage that the tool, which rotates around its own center axis, has to be relatively long and slender, particularly in those cases when the workpiece has a large diameter. This is a consequence of the fact that the rotation axis of the tool extends essentially tangentially with the workpiece and that the shape and dimensions of the tool have to be such that no parts of the tool, except the turning insert, can contact the workpiece during the machining. For this reason, it is also difficult to face turn end surfaces of workpieces using the technique disclosed in U.S. Pat. No. 7,156,006 and U.S. Pat. No. 7,325,471, particularly if the radius of the end surface is longer than the front slender part of the tool.
An object of the invention to achieve a chip-cutting metal working wherein the turning insert can achieve a long service life and thereby a long machining time. The chip-cutting metal machining should also be flexible and be applicable for the machining of different types of workpieces, particularly workpieces of a large diameter. Furthermore, the chip-cutting metal machining should be realizable by a relatively simple machine tool and in a relatively simple method.